"A composite image, combining all of the Jan 17/18 data - after cleaning up the cosmic rays and improving the S/N (signal to noise ratio) clearly shows the comet has a coma and tail," said Tony Farnham, a Deep Impact research scientist at the University of Maryland, to Universe Today.

"Not only does the total brightness of Hartley 2 vary, but the dust and gas structures in its coma show occasional 'hiccups' over the course of several rotations, phenomena characteristic of a complex rotation state," said study co-author Tony Farnham, an associate research scientist at the University of Maryland.

"Based on our observations, we calculate that at the time of the observations the comet was producing about 13 gallons or 49 litre of water each second," said Tony Farnham, a senior research scientist at University of Maryland College Park (UMCP) in the US.